1. Field of the Invention
Embodiments of the invention relate to a liquid crystal display and more particularly to a liquid crystal display displaying a black image on a display panel when an abnormal signal is input.
2. Discussion of the Related Art
Liquid crystal displays display an image by adjusting a light transmittance of liquid crystal cells in response to a video signal. An active matrix liquid crystal display switches on or off a data voltage supplied to liquid crystal cells using a thin film transistor (TFT) formed in each of the liquid crystal cells, thereby actively controlling data. Therefore, the active matrix liquid crystal display may increase the display quality of a motion picture.
In some cases, an unwanted abnormal signal may be input to the liquid crystal display. A related art liquid crystal display counts a vertical sync signal using dot clocks through a timing controller and inputs a count output to a state decision unit shown in FIG. 1, thereby detecting whether or not an abnormal signal is input. The count output corresponding to a frame frequency is previously determined as a predetermined range (for example, A to B in FIG. 2) based on the input of a normal signal. When the frame frequency (i.e., the count output) is within the previously determined normal range A to B illustrated in FIG. 2 for a predetermined period of time, the related art liquid crystal display operates in a normal state. On the other hand, when the frame frequency is beyond the normal range, the related art liquid crystal display decides that there is no normal signal. Hence, the related art liquid crystal display converts all of input video data into black data and displays a black image on a display panel.
The liquid crystal display includes a liquid crystal module including the timing controller and a system supplying various signals to the liquid crystal module. In the related art liquid crystal display, because only the timing controller has a function detecting whether or not the abnormal signal is input, a design freedom of the related art liquid crystal display is reduced. Furthermore, because the normal range has to be widely set so as to increase compatibility of the timing controller, it is impossible for a user to precisely control the related art liquid crystal display. When the user wants to use a range C to D instead of the range A to B as the normal range, an internal logic of the timing controller has to be entirely changed.
When the abnormal signal is input, the related art liquid crystal display produces the black data in the system and outputs the black data to the liquid crystal module, so as to display the black image on the display panel. In this instance, the system requires a wake-up time in conformity with a series of sequence, so as to again convert the black screen into a normal screen.